1. Field of the Invention
This invention relates generally to gaseous discharge devices and, in particular, to gaseous discharge lamps having mounting bases.
2. Description of the Prior Art
Gaseous discharge lamps are well-known in the art and are utilized in a wide variety of applications. The particular structure and configuration of the lamps also vary with the particular use for which they are adapted but, in general, all comprise a sealed transparent or translucent envelope containing a gas or vapor and include means for energizing the lamp, exciting the gaseous substance to form a radiation-emitting plasma. The energizing means most often takes the form of a pair of spaced electrodes in the envelope to which an operating voltage is applied. However, lamps of this type are also energized by means of radio frequency electric power reactance-coupled to the lamp without the need for electrodes as such.
The present invention relates particularly to lamps of the type containing a metallic vapor, such as a mercury vapor, which may be employed in situations where the particular configuration and position of the plasma, which constitutes the light-emitting portion of the lamp when in operation, is critical and its position within its installation environment is reproducible when a lamp is replaced.
A particular requirement for such a lamp is in connection with the apparatus for the exposure of photoresist-coated wafers in the production of semiconductor devices described and claimed in a co-pending application of H. S. Hemstreet et al., Ser. No. 339,860, filed Mar. 9, 1973 and assigned to the same assignee as the present invention. This apparatus requires a mercury vapor lamp of arcuate configuration, the luminous plasma of which must be very precisely positioned with respect to its operating environment as will be described in detail hereinbelow.
It is the basic object of the invention to provide a novel gaseous discharge lamp which may be installed in its operating environment so as to position the plasma with a high degree of precision.
A further object is to provide a novel gaseous discharge lamp having a mounting base which enables the replacement of lamps in their operating environments without significant deviation in the locus of the plasma relative to such environment.
Another object is the provision of a gaseous discharge lamp fulfilling the preceding objects which is quickly and easily replaceable and which automatically positions itself so that its luminous plasma occupies essentially the exact same position occupied by it predecessor.